Many fiber optic gyroscopes (FOG) use a broadband light source to provide the light that is introduced into a fiber-sensing coil for rotation detection. The induced phase shift between the counter propagating light waves injected in the fiber coil is proportional to the rotation rate. The proportionality constant, called “scale factor”, is proportional to the average, or mean, wavelength of the light source. Hence the accuracy of the gyroscope is determined by the accuracy by which the average wavelength of the light source is known.
Wavelength stabilization of the optical source has been accomplished by using a wavelength stabilization circuit (WO99/66612). Such a circuit comprises a first wavelength division multiplexer (WDM) which splits the output light of the SLED received via the optical fiber into a first band equal to a full width half maximum (FWHM) SLED bandwidth, and a second band containing a residual spectrum containing two side lobes. It also comprises a second WDM which separates the residual spectrum into a lower half centered around λ1 and an upper half center around λ2, optical detectors, and a differential amplifier responsive to the upper and lower halves so as to provide and output error signal when the upper and lower halves are not equal which is used in a feedback loop to actively control the wavelength.
Another active wavelength stabilization process is proposed in WO02/052755. The method and system are based on utilizing an optical power divider to generate two optical signals for the broadband source and a reference wavelength source. Because component aging and changes in environmental factors similarly affect the power ratios, the difference in the power ratios can be used to adjust the wavelength of the broadband source so that its center wavelength is stabilized to the center wavelength of the reference source.
An alternative approach that is more convenient to implement is described in WO99/37975. According to this disclosure, the emission bandwidth irradiated from the light source into a fiber end is to be limited to a narrower transmission bandwidth in the wavelength area of the intensity characteristic curve of the light by a narrow-band optical filter. The temperature of the filter is measured and temperature dependence of the transmission characteristics can be quickly corrected during use of the optical interference filters by means of a pre-calibrated look-up table. The readjusted wavelength value is used for calculating the scale factor.
Another approach is described in DE10307524 and WO2004074774. According to this approach, light from a superluminescent diode is coupled via a coupling element into one or two temperature stabilized bandpass filters.
All these approaches have in common that they require a relatively complicated set-up using accordingly relatively expensive components and/or a high computation power to numerically compensate inaccuracies and/or bring about high losses, which makes a solution with a small form factor and no additional electronics difficult to realize.